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A207402
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Number of n X 7 0..1 arrays avoiding 0 0 1 and 0 1 1 horizontally and 0 0 1 and 1 1 0 vertically.
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1
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20, 400, 2340, 8910, 26676, 68060, 154580, 321110, 621300, 1134296, 1972900, 3293310, 5306580, 8291940, 12612116, 18730790, 27232340, 38844000, 54460580, 75171886, 102292980, 137397420, 182353620, 239364470, 311010356, 400295720
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = (1/36)*n^7 + (4/9)*n^6 + (53/18)*n^5 + (91/9)*n^4 + (589/36)*n^3 + (31/9)*n^2 - (58/3)*n + 6.
G.f.: 2*x*(10 + 120*x - 150*x^2 + 135*x^3 - 42*x^4 - 14*x^5 + 14*x^6 - 3*x^7) / (1 - x)^8.
a(n) = 8*a(n-1) - 28*a(n-2) + 56*a(n-3) - 70*a(n-4) + 56*a(n-5) - 28*a(n-6) + 8*a(n-7) - a(n-8) for n>8.
(End)
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EXAMPLE
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Some solutions for n=4:
..0..0..0..0..0..0..0....0..1..0..1..0..0..0....1..1..1..1..1..1..1
..1..1..1..0..0..0..0....0..1..0..1..0..0..0....0..1..0..1..0..0..0
..0..0..0..0..0..0..0....0..1..0..1..0..0..0....1..1..1..1..1..1..1
..1..0..0..0..0..0..0....0..1..0..1..0..0..0....0..1..0..1..0..0..0
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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